aaaaargh!
2. Secret base at ground level or even underground.
3. Needs some street level work
4. Two or three glass elevators running down the building in different places, perhaps a flooded vent that you can take a really big dive into...
Nobody is suggesting you make the secret base inside the tower...
If that doesn't cause you huge bsp problems, why not, but bear in mind you need to give the players a sense of where they are, i.e. windows etc...
I feel the map would benefit from a cityscape skybox and also buildings around the map edge, not just a black wall...